The present invention relates to an ultra-high frequency tuning device incorporating a part which is fixed relative to the wall of a cavity and a moving part which slides within the fixed part so that it can more or less deeply penetrate the said cavity. A good quality electrical contact between the fixed part and the moving part must ensure the passage of surface currents between these two parts.
Such devices are known, e.g. from U.S. Pat. No. 2,556,607 in which elastic plates fixed to one of the parts ensures a sliding contact with the other part. These plates are made from materials having a good elasticity but, as a result, are hard, fragile, abrasive and poor conductors of electricity. To obviate these defects it is known to cover such elastic plates with a deposit of silver or gold by electrolysis, which is a good conductor of the ultra-high frequency currents forming the surface currents. However, since for mechanical strength reasons, the moving part must be made from a metal whose hardness is greater than that of silver or gold, the repeated displacements of the moving part within the fixed part bring about a rapid deterioration of the surface state, i.e. of the gold or silver deposit, due to friction. This is the case, for example, when such a device is used in a frequency-mobile filter, i.e. in a filter which has to operate in several frequency ranges or channels and which must be able to pass rapidly from one range or channel to another. This rapid deterioration of the surface state leads on the one hand to a progressive reduction in the quality of the filter with, in particular, an increase of losses and the appearance of "undesired noise" during tuning changes and on the other hand to a limited service life.